1. Field of the Invention
The present invention relates to a manufactured building system and more particularly pertains to constructing partially prefabricated homes and school classrooms that can be easily transported and assembled.
2. Description of the Prior Art
Generally, the manufactured building systems available in today=s market incorporate designs and materials that have not been changed or improved for more than 30 years. Most transportable manufactured homes are built with conventional building materials such as wood stud frames, fiberglass batt insulation, wood siding, wood floors, wood roof trusses, asphalt roof shingles and a steel trailer frame with permanently attached wheels for transport from the factory to the building site. The weights of the materials used in the construction are relatively heavy when compared to the weight of the floor system or foundational materials resulting in a top-heavy structure with a high center of gravity. This is contrary to good engineering practice wherein it is known that a heavy foundation is needed to overcome the overturning, uplift and sliding forces exerted by high winds.
Because of the permanently attached wheels and steel trailer frame that also supports the wood floors, most manufactured buildings are erected on the building site by jacking the building up and placing concrete blocks under the trailer bed at specified locations. The building is then lowered onto the concrete block piers. The wheels remain attached to the steel trailer bed. This erection method results in a building that has the floor system elevated two to three feet above the ground. The space around the bottom of the building is enclosed around the perimeter with fencing, blinds, skirts or other apparatus designed to hide the concrete block piers and steel trailer bed from view. This type of building system is commonly referred to as the “trailer look”.
Because of the lightweight of the steel trailer bed, and other foundational elements, there is little resistance to high wind loads and the building can easily be blown off of the concrete piers during high winds. To prevent this problem, the manufacturers of this type of building system have devised an anchoring system that is intended to hold the building down to the concrete piers in order to resist overturning, uplift and sliding forces generated by high winds. The anchor system is comprised of steel rods that are driven into the ground to a specified depth and at specified intervals. Steel straps are then connected between the rods and the underside of the steel trailer bed and tensioned by means of a turnbuckle or other device that stretches the steel straps to exert a downward force on the building assembly. The manufacturers claim that this system is adequate to prevent uplift or overturning of their buildings during high winds and the applicable building codes are written to include tie-down straps as a condition precedent to the issuance of a certificate of occupancy.
Although the manufacturers claim that the tie down straps adequately withstand the wind loads, it is well known that conventional manufactured buildings are not safe for habitation during high windstorms. Although the tie down strap system offers some improvement in the structural strength of the building, it does not achieve the degree of structural strength that is needed to withstand hurricane force winds or that would be achieved with a floor system or foundation that is heavier than the structure above.
The wall construction of conventional manufactured buildings is generally comprised of wood studs with fiberglass batt insulation between the studs. The exterior side of the wall is generally covered with oriented strand board (OSB) and the interior side with gypsum board (drywall). The overall thickness of these walls is approximately 4 inches.
Because the walls are constructed with wood studs and are insulated with fiberglass insulation installed into a 4-inch thick cavity there are two resultant deficiencies. The most obvious deficiency is the highly flammable wood construction. These buildings burn very fast and are a fire hazard for the occupants. The second is the energy efficiency. Generally it is not possible to achieve an insulation or R-value greater than an R-11 with the 4-inch thick wall. These buildings are generally not very energy efficient.
Walls constructed with wooden materials are flexible and do not achieve the structural strength that can be achieved with other building materials such as steel, concrete or composite building panels. This places limits on the wind loads that a wood stud wall can withstand. In order to increase the strength of wood stud buildings to withstand the constantly increasing building codes it is necessary to include more studs spaced closer together in the wall. This increases the cost of construction and consumes more of our precious natural resource.
The roof system of conventional manufactured buildings is generally constructed with a wooden truss system. A wooden truss is a generally triangular shape with a bottom part that is flat and is connected from one side of the building to the opposite side of the building parallel with the floor. The two sloping halves of the roof are connected at the outermost side of the bottom part and slope upward to the connection at the roof ridge to form a triangle. Since the outside of the roof truss is covered with roofing materials such as plywood and shingles and the inside of the roof truss is covered with drywall, a cavity is created on the interior sides of the roof truss.
There are three problems inherent in this design. The first problem is with the excessive amount of heat that is known to build up inside the cavity. The open space inside the truss serves as a container that captures heat similar to an oven. This requires the building designers to incorporate a means to ventilate the heat to the building exterior. Although some heat can escape to the outside of the building through attic vents, most of the heat remains inside the roof truss cavity and escapes to the buildings interior. This places an excessive load on the air conditioning system and is not an energy efficient design.
The second problem is with the uplift forces exerted on a roof truss system during windstorms. It is well known that roof systems that are not made an integral and structural part of the overall building envelope can be blown off and separated from the building during high winds. Therefore the building manufacturers must incorporate a means to adequately tie the truss system to the outside walls of the building with straps or other means of mechanically fastening the truss system to the building walls. This is generally accomplished with tie down straps or truss brackets. Although these devices offer some resistance to uplift forces, it is generally known that this remains a weak part of the overall structure.
The third problem is that most roof trusses are constructed with wooden materials. As with the exterior walls this creates a fire hazard.
Roof trusses constructed with wooden materials are flexible and do not achieve the structural strength that can be achieved with other building materials such as steel, concrete or composite building panels. This places limits on the wind loads that a roof truss can withstand. In order to increase the strength of roofs constructed with wooden trusses to withstand more stringent and constantly increasing building codes, it is necessary to include more trusses spaced closer together. This increases the cost of construction and consumes more of our precious natural resource.
The floor systems of conventional manufactured buildings are generally constructed with wooden floor joists that are supported underneath with a steel trailer body constructed with steel channels and angles. The wooden joists are covered on the topside with oriented strand board or plywood panels. This floor system is relatively lightweight and does not achieve the structural strength that is found with a concrete floor.
A wooden floor system is relatively flexible and cannot support the weight of heavy objects such as refrigerators, dressers and other interior furnishings. Over time, these floor systems have a tendency to warp or bow from the furniture and other dead and live loads placed upon them.
A wooden floor system can burn easily and rapidly. This creates a fire hazard for the building occupants.
It can be thus appreciated that the use of manufactured building systems of known designs and configurations is known in the prior art. More specifically, manufactured building systems of known designs and configurations previously devised and utilized for the purpose of constructing buildings by known methods and apparatuses are known to consist basically of familiar, expected, and obvious structural configurations and building materials, notwithstanding the myriad of designs encompassed by the crowded prior art which has been developed for the fulfillment of countless objectives and requirements.
By way of example, U.S. Pat. No. 5,373,678 to Hesser issued Dec. 10, 1994, relates to a structural insulated building panel. Hesser teaches a building panel that incorporates an internal stiffener stud that can be formed through the manufacturing process simultaneously with the exterior steel skins and polyurethane foam core. Hesser further teaches a means of connecting the building panels together with hand formed metal sheets and screws to form the walls and roofs for various buildings. There are limitations with this design because the hand made bent metal shapes cannot me made in long lengths and are not structurally strong. They cannot be made with in integral thermal break and a multitude of screws are required to connect the metal shapes to the thin skin of the building panel. The assembly design depicted in the Hesser patent is labor intensive, which results in excessive cost for material fabrication and erection. The Hesser design is not structurally strong because the metal shape itself does not control the positive and negative wind loads exerted on a building. The loads are exerted fully on the multitude of screws connecting the metal shape to the panel. Hesser does not teach an extruded aluminum connector system that can be manufactured in long lengths. Hesser does not teach an extruded aluminum connector system that includes an integral thermal break and that is adjustable to accommodate various roof pitches and vertical wall angles. Hesser does not teach an extruded aluminum connector system that is connected to the building panels with through bolts or that control the positive and negative wind loads through the connector itself. Hesser does not teach a manufactured building system that can be transported on a self-trailering multi-stemmed concrete floor system.
U.S. Pat. No. 5,509,242 to Rechsteiner issued Apr. 23, 1996, relates to a structural insulated building panel system. Rechsteiner teaches a building panel that is reinforced by inserting steel angles, by hand, into the open edge after the panel is manufactured. This method of reinforcing a building panel is costly, due to higher material costs, and labor intensive, due to inserting the pieces by hand. Rechsteiner further teaches a method of connecting the panels together with the same hand made bent metal shapes taught in Hesser. In fact the only difference between Hesser and Rechsteiner is the method of reinforcing the building panel. Rechsteiner has the same limitations with the assembly of the building panels as described above in Hesser.
U.S. Pat. No. 6,101,779 issued on Aug. 15, 2000 to Davenport teaches a pre-cast concrete slab having a multi-bayed construction. The concrete slab depicted here relies on a multitude of beams, purlins and ribs to form a supporting structure that are reinforced with deformed reinforcing bar steel (rebar). The concrete slab depicted here is formed by laying a multitude of steel channels in different directions to provide a trough for forming the concrete. Many Styrofoam blocks are laid out between the steel channels to provide additional forming members for the concrete. In order to provide longitudinal support sufficient to hold the concrete together and avoid cracking during transport, a considerable amount of steel rebar and wire mesh is laid out on top of the steel channels and Styrofoam forms. The method of constructing the pre-cast concrete slab depicted in Davenport uses an excessive amount of steel that is all placed by hand. This results in excessive material and labor costs. In fact, the concrete slab taught by Davenport is really the same steel support frame used in the manufactured building segment for the past 30 years but with concrete poured on the top. Furthermore, the steel bottom channels are exposed which makes the support frame susceptible to rust and corrosion.
For transport, the Davenport concrete slab must be lifted and placed on a steel trailer or bogey with wheels located at the front and rear of the unit. The wheels are not able to be located partially within the open spaces under the slab because of the multitude of cross beams, purlins and ribs formed to provide lateral support of the concrete. This causes the slab to be located above the height of the wheels and steel forming the trailer or bogey frame thereby increasing the space between the bottom of the slab and the roadway during transport. This causes the center of gravity to be higher than is desirable and limits the overall building height for passing under bridges and utility lines.
Davenport does not teach a multi-stemmed concrete floor that is manufactured by the pre-stressing method. Davenport does not teach a multi-stemmed concrete floor that transfers all of the longitudinal live and dead loads to a reinforced diaphragm header. Davenport does not teach a multi-stemmed concrete floor that is manufactured entirely of concrete and does not rely an exposed steel frame for structural support. Davenport does not teach a multi-stemmed concrete floor that is transported by attaching a wheel assembly directly to the down turned stems. Davenport does not teach a multi-stemmed concrete floor that has wheels located on only the rear end. Davenport does not teach a multi-stemmed concrete floor that minimizes the clearance between the roadway and bottom side of the floor by concealing the upper ⅓ of the wheel within the open spaces between the down turned stems. Davenport does not teach a multi-stemmed concrete floor that is manufactured in a self-stressing steel form with a removable stressing block.
U.S. Pat. No. 3,944,242 issued on Mar. 16, 1976 to Eubank addresses the center of gravity problems inherent to a movable building, such as a prefabricated house and with the deficiencies inherent with pre-cast slabs as taught in Davenport. Eubanks teaches a concrete slab wherein the structural reinforcement of the concrete is made by the post-tensioning method, which is preferred to pre-casting. Although Eubanks refers to pre-stressing, a method of pre-stressing is not demonstrated by Eubanks. Eubanks teaches a concrete slab that is reinforced by post-tensioning in both the longitudinal and lateral directions. Without the lateral tensioning the Eubanks slab would easily break apart during transport. The forming bed depicted by Eubanks shows a form that has the two long side and two short side blocks forming the outer edge of the slab connected to a multitude of hydraulic rams. This allows the sides to by pulled away from the slab edges after the concrete has been poured and cured. It is necessary to make the sides removable in order to have access for the insertion and tensioning of the internal tensioning rods in both the longitudinal and lateral directions. The casting form depicted by Eubanks cannot be used to make a pre-stressed slab because the sides would collapse from the stress imposed by the stressing strands used in the pre-stressing method. Also, the tensioning of the slab after it has been cast and while it is still in the form would cause the inside face of the outermost side and end stems to be tightly compressed against the form thereby causing the slab to bind against the form and making it impossible to remove. This is why the Eubanks design never became commercially viable.
The method of transport depicted in FIG. 5 of Eubanks requires the use of a large and very heavy steel support frame to connect the multitude of wheels and axles depicted here. The method of transport depicted in FIG. 4 of Eubanks shows a wheel assembly connected to the outermost longitudinal stem with one wheel on the inside and one wheel on the outside. The outside wheel causes the overall width of the unit to be increased by approximately 12″ on each side. This is not desirable because the overall width of the slab that can be transported over the highway is limited by the DOT regulations for maximum allowable widths. This results in a slab that is two feet less than what may be required.
Eubanks does not teach a multi-stemmed concrete floor that has several longitudinal stems running in a parallel direction. Eubanks does not teach a multi-stemmed concrete floor with a reinforced diaphragm header. Eubanks does not teach a multi-stemmed concrete floor that is reinforced by pre-stressing in only the longitudinal direction. Eubanks does not teach a multi-stemmed concrete floor that does not require post-tensioning or pre-stressing in the lateral direction and that is entirely reinforced in the lateral direction through the reinforced diaphragm header. Eubanks does not teach a pre-stressed concrete floor. Eubanks does not teach a multi-stemmed pre-stressed concrete floor that is manufactured in a self-stressing steel form. Eubanks does not teach a multi-stemmed concrete floor that is manufactured in a steel form with permanently fixed long sides and a removable stressing block. Eubanks does not teach a multi-stemmed concrete floor casting form that relieves the compressive forces exerted on the casting form with a compressible filler assembly. Eubanks does not teach a multi-stemmed concrete floor that is transported by attaching a wheel assembly directly to the interior longitudinal stem with the wheels inside the outer extents of the floor thereby allowing the concrete floor to be manufactured to the maximum width that can be safely transported over the highway.
As can be seen with the cited patents, some attempts have been made to overcome the inherent problems and deficiencies found with conventional manufactured homes and school classrooms but none has solved the aforementioned deficiencies. Reference is made to U.S. Pat. No. 5,373,678 to Hesser, U.S. Pat. No. 5,509,242 issued to Rechsteiner, U.S. Pat. No. 6,101,779 issued to Davenport, U.S. Pat. No. 3,944,242 issued to Eubanks, etc.
While these devices fulfill their respective, particular objectives and requirements, the aforementioned patents do not describe a manufactured building system that allows constructing partially prefabricated homes and school classrooms that can be easily assembled and constructed with a structural aluminum connector system and transported on a multi-stemmed pre-stressed concrete floor system.
In this respect, the manufactured building system according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in doing so provides an apparatus primarily developed for the purpose of constructing partially prefabricated homes and school classrooms that can be easily transported and assembled and solves all of the problem inherent in the prior art.
It should be noted that the present invention utilizes the pre-stressing method of strengthening concrete. Pre-stressing greatly strengthens and improves the ability of the concrete material to withstand cracking during transport by putting the fully cured concrete element under compression. It is well known that concrete is strong in compression but weak in tension. The pre-stressing method of reinforcing concrete is also well known and has been utilized to manufacture double T bridge slabs, tilt-up wall slabs, roof slabs, building pilings and other such elements for many years. Therefore, the pre-stressing method itself is not being claimed herein as new art or part of this invention.
What is being claimed and made a part of this new invention is the application and use of the pre-stressing method in a new and innovative way. The prior art of reinforcing concrete elements by the pre-stressing method has been applied principally to the manufacture of double-stemmed concrete slabs for bridge and tilt-wall building construction. These slabs are manufactured in long lengths up to 60 feet long and short widths up to eleven feet wide. The two down turned stems are spaced approximately five feet apart and are manufactured from 12″ to 36″ high by 4″ to 8″ wide and are joined together across the top surface or web with a concrete flange that is 2″ to 4″ thick. They are open on the short ends with the cross sectional design clearly visible.
Because the relatively thin 2″ to 4″ thick flange is the only material connecting the two stems together, the slab must be moved out of the casting form by placing lifting loops at each end of the stems for a total of four lifting points. Great care must be taken to lift the stems in a parallel orientation to one another without bending or twisting which would cause the thin flange to break or crack. The thin 2″ to 4″ thick flange is incapable of supporting the weight of additional stems. During transport from the manufacturing plant to the erection location, the stems must be supported at equal heights and parallel to one another at each of the four ends. Furthermore, the relatively wide space between the stems requires the height of the stems to be relatively high in order to provide the structural strength needed to manufacture long lengths.
The present invention solves the problem of cracking or breaking the weak 2″ to 4″ flange by casting a reinforced diaphragm header integrally with multiple down turned stems. The diaphragm header conceals the cross sectional design from view and creates a closed end. Multiple down turned stems can be connected to the diaphragm header and eliminate the bending and twisting forces that are exerted on the flange in the double stem design. This enables the entire multi-stemmed concrete element to be lifted from the same four points as in the concrete element to be lifted from the same four points as in the double stem design but without cracking or breaking the flange because the diaphragm header supports the weight of all of the stems. The stems can also be placed closer together to allow a reduction in the overall height. All of the manufacturing problems caused by the compressive forces exerted by the pre-stressing method and resulting in shrinkage of the finished element have been overcome by the present invention and will be clearly explained by the diagrams, descriptions and claims made herein.
Therefore, it can be appreciated that there exists a continuing need for a new and improved manufactured building system, which can be used for constructing partially prefabricated homes and school classrooms that can be easily transported and assembled. The present invention can withstand hurricane force winds and is highly energy efficient as well as being insect and fire proof. The present invention further has a concrete floor and can withstand impact from large flying missiles. In this regard, the present invention substantially fulfills this need.